Turbine nozzles are common components of Gas Turbine Engines (GTE). The purpose of a turbine nozzle is to meter and accelerate combustive gas flow, while turning the gas flow towards the blades of a turbine rotor located immediately downstream of the turbine nozzle. To serve this purpose, a turbine nozzle contains a number of airfoil-shaped vanes, which are arranged in an annular array extending between inner and outer annular endwalls. During GTE operation, the turbine nozzle vanes are bathed in combustive gas flow and consequently subject to high thermal loads, pronounced thermal cycling, and rapid gas velocities. This is particularly true in the case of a High Pressure (HP) turbine nozzle, which is positioned immediately downstream of the GTE combustor and thus directly exposed to combustive gas flow at peak temperatures and velocities. For this reason, it may be desirable, if not necessary to provide cooling to the turbine nozzle vanes and, specifically, the leading edge regions of the turbine nozzle vanes. Such cooling is intended to prevent premature failure of the turbine nozzle vanes, while allowing operation of the GTE at relatively high combustor outlet temperatures.
Vane impingent tubes can be utilized to cool the leading edge portions of the turbine nozzle vanes. Generally, vane impingement tubes are inserted into the hollow bodies of the turbine nozzle vanes through openings in the outer annular endwall. When supplied with secondary cooling airflow, the vane impingement tubes direct cooling jets against interior surfaces of the leading turbine nozzle vane regions to convectively remove heat from the nozzle vanes and provide the desired impingement cooling effect. Additional heat may also be convectively transferred to the cooling airflow as the air flows along the interior surfaces of the turbine nozzle vane, as well as conductively transferred to the vane impingement tubes via contact with ribs or other internal structures of the turbine nozzle vanes. Overall, the usage of such vane impingement tubes can provide a highly effective internal impingement cooling scheme, which maintains the turbine nozzle vanes at sufficiently low temperatures to avoid premature structural failure and prolong the serviceable lifespan of the turbine nozzle. The enhanced cooling afforded by the vane impingement tubes may be hindered or entirety thwarted, however, should there develop a blockage or occlusion impeding airflow through one or more of the impingement tubes.